\begin{slide}{violet}
\violet
much is known about exact solution:
\begin{itemize}
\item all N-points are of degree 1, 2, or 3
\item all S-points are of degree 3
\item any two edges meet in an angle of at least $120^o$
\item there are at most N-2 S-points
\item the problem is NP-hard (exact solutions will almost certainly 
require exponential time)
\end{itemize}
\end{slide}

